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Unusual CRT monitor screen symptom no one has been able to recognize (yet)


chaos199
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I have a kortek KTX-26 chassis and Zenith CRT from a LAI NEO-GEO cabinet (and it was used in a lot of LAI early 90’s cabinets). A have 2 NEO GEO 6 slot cabinets (both left unused in storage for 15 years) so to isolate the cause I swapped the MV6 board, game power supply, chassis, game carts and even ran the power cable to the chassis from the other cabinet but trying all these thing never made a different so I believe it must be the CRT or interference from something. My other identical NEO cabinet works fine and the filament in the CRT neck is just as bright. One technician said it likely be a high voltage problem without seeing it. There is no arching at all. I went through a huge monitor repair guide consisting of over 115000 words (http://repairfaq.cis.upenn.edu/sam/monfaq.htm) but unfortunately nothing was mentioned that fit my symptom (but I did learn plenty of other things from it).

 

The effect on the screen is flickering rectangle dots that consistently flash all over the screen. I haven’t noticed a pattern, it just seem to flicker/flash like rain drops. The dots are white and they become more or less noticeable depending on how bright the screen is with video graphic changes. It is most noticeable when the screen changes between bright and dark - like when the NEO GEO logo pops up on the screen. Changing the G2 control on chassis does not fix the issue and will only alter how noticeable it is when the screen is dark or not (which is useless with video game graphics constantly changing. I have read power source can give interference even if from down the street but unsure why my other cabinet is not effected.

 

It would be really great if someone could give me advice on how to fix this monitor issue or at least has heard or read of it happening to someone else (hopefully on this site), and the name of the symptom (if it has ever been given one) as it may give me a new direction to search for. I will attach a link to some tiny mp4’s to notice the flashing tiny horizontal lines (never mind the vertical lines in the logo vid as I have since fixed that glitch). I am very surprised that with so many users on the site with arcades I can’t find any post mentioning the same type of issue.

 

https://drive.google.com/file/d/11E7JFgL2vhl2mmk-dqZDwBKXXuMVUdhZ/view?usp=sharing

 

https://drive.google.com/file/d/1F15Dy-EeI5YdxeTGHwKI79urjyvgmcws/view?usp=sharing

 

https://drive.google.com/file/d/10OxvfDrQvX7yVynHZqDOEM8BZX5S-lZW/view?usp=sharing

 

 

 

neo.mp4 - Google Drive

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I did note that the vertical lines graphic glitch has since been fixed and I do have 2 complete identical cabinet and systems to compare with. Take a look at all 3 vids and you will see (the neo logo vid is an old one but still contains the main issue with fault).
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Hard to tell from the videos but it looks like it may be external interference that is causing this. If you turn off absolutely everything nearby does it improve at all? e.g. all lighting, (LEDs and Fluorescent lighting is incredibly noisy) and any appliances running nearby can also have an effect, even if they seem to be doing nothing at the time.

 

If it can be isolated to a specific external source then we can work out why one monitor is more susceptible than the other.

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everything is turned off in my house except the fridge and clock but it makes no difference. It's weird how when both identical cabinets are turned on at the same time only one is still effected (even when I swap the monitor power cables to the chassis from the other cabinets putting them back to back). In last 24 hours 3 qualified repair techs (including Jomac) have told me the cause is different. One said it was a HV chassis problem, another said it was the CRT and can not be fixed and another said it was simply a ground/earthing issue. I hope there is a user on AA that has actually had this problem and solved it.
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The only thing that makes much sense out of that list to me is the grounding/earthing issue. I've seen interference (shimmering lines) when either...

 

1) the PSU output ground is also connected to the mains input earth.

2) The chassis is connected to earth.

 

If you have either of those i would suggest temporarily disconnecting them and seeing if it cures the problem.

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Thank God (or should I say AA users) I finally fixed the problem simply by unscrewing the ground braid to the chassis. I don't know why LAI made it like that or what happen to cause the problem but removing it solved the problem
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In last 24 hours 3 qualified repair techs (including Jomac) have told me the cause is different. One said it was a HV chassis problem, another said it was the CRT and can not be fixed and another said it was simply a ground/earthing issue. I hope there is a user on AA that has actually had this problem and solved it.

 

It was Jomac that told you it was a Ground/Earthing issue, it is very common and not at all usual, discussed countless times in this forum and why I suggested you look on here.

Whoever told you it was a HV chassis problem or the CRT has no idea what they are talking about and are not qualified repair techs.

The reason you couldn't find the name of the issue is because it is not a monitor fault and there is no reason it would need to included in any repair manual etc, it is simple interference being displayed on the monitor.

 

This issue is explained in depth, these are a couple of threads there many more.

 

https://www.aussiearcade.com/forum/arcade/arcade-technical-and-repair-questions/104052-can-anyone-diagnose-my-crt-image

 

https://www.aussiearcade.com/forum/aussie-arcade-sponsor-s-trading-forum/arcade-pinball-and-amusement-machine-sponsors/jomac/62598-very-faint-squiggly-line-left-side-of-screen?highlight=#post1089652

 

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On my previous post i did mention I fixed my problem - thanks to advice from AA users (which of course includes Jomac as a user). That info I got from other other techs stating it was a HV and crt problem have websites claiming to be expert qualified repairers of TV's and other electronic goods. Hey Jomac, they may met the bare minimum requirements to be qualified but perhaps they are just exaggerating theirs skills and aren't no where near as good as you Jomac. Maybe they just wanted to make it up as if it was a much more serious problem then it was so I would have to drop it off to them as they asked me to, and they could bill me plenty for a 10 second job without me really ever knowing what was wrong with. People might do some immoral things during covid-19 with a loss of income. Thanks for the extra links

 

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